Voltage regulators are used in applications which require a well controlled voltage. Voltage regulators need to be carefully designed to maintain proper behavior over the frequency range of operation. The presence of poorly located poles in the frequency response of a voltage regulator may lead to unstable operation of the voltage regulator. Conventional voltage regulators with a two-stage operational amplifier (op-amp) achieve stable behavior over the frequency range of interest by using a technique known as “pole splitting”. This technique separates the two poles of the op-amp by moving one pole to a lower frequency and the other pole to a higher frequency. The lowest frequency pole is called the dominant pole because it dominates the effect of the higher frequency poles.
Voltage regulators implementing pole splitting compensation place a resistor and a compensation capacitor in series between the first and the second stage of the op-amp to create the dominant pole at the first stage of the op-amp due to Miller capacitance. The higher frequency pole of the voltage regulator is dependent on the output load capacitance, which in turn depends on chip density and transistor capacitance junction loading.
There are two significant drawbacks to this pole splitting compensation technique. To achieve a dominant pole at low enough frequency, a large compensation capacitance is required, which slows down system response time. The second drawback is the output pole location is changing due to changing of capacitance or current load. This leads to difficulty using a single voltage regulator design for a family of circuits where the output capacitance varies between different designs. In this case, a designer has to tune and verify the voltage regulator performance for each design.
It is in this context that embodiments of the invention arise.